opencascade qml QQuickItem offscreen FBO

[kndpeng]

I modify AndroidQt, but the display area alway display left bottom corner.
JSlyadne says: you'll need to utilize another approach and deal with frame buffer rendering.
Can anyboy give me a example or a clue?

 

[JSlyadne]

Please, point out what version of Qt\Qml you use as it makes a big difference since Qt 6.

 

[kndpeng]

Please, point out what version of Qt\Qml you use as it makes a big difference since Qt 6.

I download code from qml occt(https://github.com/ShabalinAnton/opencascade_qml.git)
I changed some code. I want qquckitem can location anywhere, but qquckitem view always locate left bottom.

I use qt 5.12.10; opencascade 7.8.
How to bind opencascade offscreen FBO?

 

[JSlyadne]

The sample you rely on initializes the OCCT viewer by giving it the id of the main window what means the OCCT viewer uses the canvas of the main window for rendering, and changing the size of the host item (OcctViewer item) has an impact on the camera view.

this->initializeViewer(Aspect_Drawable(this->window()->winId()));

Approaching FBO will allow you to make OCCT to render on a specific area of window. To achieve this you should substitu OcctViewer with own implementation which will inherit QQuickFramebufferObject. Look at this (https://code.qt.io/cgit/qt/qtdeclarative.git/tree/examples/quick/scenegraph/fboitem?h=6.5) as an example.

 

[JSlyadne]

Below is another sample code where OcctFramebufferObject is an item to render on and OcctViewer is a class wrapping OCCT rendering capabilities (initializes window, context, view(s), etc.)

class OcctFramebufferObject: public QQuickFramebufferObject
{
...

private:
class FboRenderer;
}

class OcctFramebufferObject::FboRenderer : public QQuickFramebufferObject::Renderer
{
public:
FboRenderer();

protected:
void synchronize(QQuickFramebufferObject* fboViewer) override;
QOpenGLFramebufferObject* createFramebufferObject(const QSize& size) override;
void render() override;

private:
OcctViewer m_renderer;
};

OcctFramebufferObject::FboRenderer::FboRenderer()
: Renderer()
{
}

void OcctFramebufferObject::FboRenderer::synchronize(QQuickFramebufferObject* fboViewer)
{
auto* viewer = qobject_cast<OcctFramebufferObject*>(fboViewer);
if (viewer == nullptr)
return;

// The right place for passing data from GUI to Rendering thread
...
}

QOpenGLFramebufferObject* OcctFramebufferObject::FboRenderer::createFramebufferObject(const QSize& size)
{
QOpenGLFramebufferObjectFormat format;
format.setAttachment(QOpenGLFramebufferObject::CombinedDepthStencil);
format.setInternalTextureFormat(GL_RGB8);
format.setSamples(4);
return new QOpenGLFramebufferObject(size, format);
}

void OcctFramebufferObject::FboRenderer::render()
{
const QOpenGLFramebufferObject& fbo = *framebufferObject();
m_renderer.setSize(fbo.width(), fbo.height());
m_renderer.render(fbo.handle()); // Do rendering stuff here
}

 

[kndpeng]

Thank you. I know how to achieve it.